An intra-aortic balloon pump (IABP) comprises an intra-aortic balloon (IAB) and a pump device, wherein the IAB can be introduced for example into the aorta of a patient whose heart does not function properly.
With every cardiac cycle, the IAB is inflated by means of a pump device at the end of an ejection phase of the left ventricle of the heart and deflated again before the next ejection phase begins. In this way, the pump action of the heart is improved and there is an improvement of the blood supply to the coronary artery. For a correct operation it is of importance that the IAB be inflated and deflated at the correct times in the cardiac cycle. In particular the correct timing in the cardiac cycle of the inflation of the balloon is very important, because premature inflation of the IAB, before the end of the ejection phase of the heart, can cause the ejection phase of the heart to stop, as a result of which the blood flow rate is reduced. In the case of too late inflation of the IAB, its operation will be less effective. The blood volume that is pumped by the IAB to the coronary arteries and to the vascular system will be smaller in that case, and the reduction of the after load on the heart during the ejection phase will be smaller.
The times of inflation and deflation of the IAB can be set manually at fixed times within the cardiac cycle by a skilled person, for example on basis of the electrocardiogram (ECG) of the heart. A disadvantage of this system is that the times that have been set will deviate from the desired times with every acceleration or deceleration of the cardiac cycle, so that said times constantly need to be reset. Furthermore it is impossible to take into account the possibility of an irregular cardiac cycle, which often occurs with those people for whom the IABP is intended. Thereby, in particular the setting of the inflation time of the IAB is carried out incorrectly in many cases.
U.S. Pat. No. 4,809,681 discloses an apparatus for controlling an IABP which determines the time at which the IAB is to be deflated on the basis of the ECG. However, the time at which the IAB is to be inflated cannot be determined by means of said apparatus.
From Sakamoto et al, ASAIO Journal 1995, pp. 79–83, there is known an apparatus which predicts the position of the incisura point in the cardiac cycle—i.e. the closing time of the heart valve—on the basis of the ECG and by computing the duration of the ejection phase from the period of time of the preceding heartbeat. Said apparatus is not accurate enough in those cases where the heartbeat is irregular.
U.S. Pat. No. 5,183,051 discloses a device by means of which it is attempted to determine the incisura point by looking for a dip in the arterial pressure signal within a predetermined time interval within the cardiac cycle. Said device is not accurate enough in the case of a damped blood pressure signal or in the case of irregular heartbeats. Furthermore, no mention is made in said document of an apparatus for controlling an IABP.
WO 9724690 discloses an apparatus which determines the closing time of the aortic valve by means of a Windkessel model. Said apparatus also functions in those cases where the heartbeat is irregular. However, even a correct determination of the closing time of the aortic valve (incisura point) results in a too late inflation of the intra-aortic balloon due to the mechanical properties of an IABP system.
The object of the invention is to provide an apparatus of the above-mentioned type which does not exhibit the above drawbacks.